EP0029705B1

EP0029705B1 - Status reporting system and data transmitters for use in such a system

Info

Publication number: EP0029705B1
Application number: EP80304144A
Authority: EP
Inventors: Louis Cecil Metz; Leroy Arthur Prohofsky
Original assignee: Sperry Corp
Current assignee: Sperry Corp
Priority date: 1979-11-23
Filing date: 1980-11-19
Publication date: 1984-10-31
Also published as: JPS5687960A; CA1157544A; DE3069567D1; US4360912A; EP0029705A1

Description

The present invention is concerned with distributed transmission systems for interrogating the status of a number of remotely distributed data points. Such systems may exist in large buildings or on board a ship or a plane, and the status information may consist of whether a hatch is open or closed, the temperature of a thermostat, etc. In such systems, the individual data points are usually coupled to the processor on separate data buses, or several data points may be multiplexed on one bus, but only one data point is interrogated at a time. An example of such a system is disclosed in U.S. patent number 4 047 159 for remotely monitoring experimental instrumentation. Such systems are relatively costly, and require a great deal of hardware duplication for each channel and sub-channel, and also require additional buffering and polling hardware.
The present invention provides a status reporting system including a bus system for monitoring the status of a plurality of geographically distributed data points, in which each data point produces a digital response signal representing some physical state, such as whether an electrical contact is open or closed, or the status of an analogue device.
The bus system comprises a plurality of transmitters, each of which is coupled to one of a plurality of buses. These buses are coupled to a processor by a signal processing and bus multiplexing device which transmits interrogation signals along the buses to the transmitters and returns their responses serially to the processor, as set out in claim 1 below. For brevity, in the description which follows the signal processing and bus multiplexing device will be referred to simply as a bus multiplexer.
Each of the buses may consist of a twisted pair cable over which the interrogation and response information are communicated, and it may be configured either in an open or in a closed loop.
The transmitters may be of two types, single point or multiplexed, and each may compare the interrogation signals to a strapped address and supply a repsonse signal to the bus multiplexer. Each single transmitter may include a presettable counter and timing circuity which recognises its own interrogation signals and inserts the response signal on the bus at the appropriate time. Each single transmitter may also produce an output which may be used to indicate the data point's status at an intermediate monitor station or which may perform some operation, so that the transmitter also functions as a data receiver.
The multiplexed transmitters may be similar to the single transmitters but may each also contain a decoder, a register and multiplexer for distinguishing between the localized data points coupled to it and for distinguishing its data points from all others in the system.
The invention will now be described with reference to the accompanying drawings, in which

Figure 1 is a block diagram of a system according to the invention.
Figure 2 is a functional block diagram of the bus multiplexer.
Figure 3 is a circuit schematic of the bus multiplexer.
Figure 4 is the timing diagram for a single interrogation cycle of the bus multiplexer.
Figure 5 is a functional block diagram of a single point transmitter.
Figure 6 is a circuit schematic of the single point transmitter.
Figure 7 is a functional block diagram of a multiplexed data point transmitter.
Figure 8 is a circuit schematic of the multiplexed transmitter.
Figure 1 represents schematically a modular, reconfigurable bus system for interrogating a number of geographically distributed data points, where each data point consists either of a single electrical contact which may be open or closed, or of an analogue transducer having its outputs converted to a digital signal. The system operates under the control of a processor 2, which transmits interrogation signals to a bus multiplexer 4, causing the bus multiplexer 4 to interrogate the status of all the data points coupled to the communication buses 6 having an address corresponding to the interrogation signals. The multiplexer, on receipt of the interrogation signals, reproduces the signals in an appropriate manner and transmits the modified signals to all of the single point and multiplexed transmitters 8 where they are compared to a strapped address, A, and if a match occurs, that data point's status response signal is transmitted back to the bus multiplexer 4. The bus multiplexer 4 then serializes the individual response signals and transmits the serial response signal to the processor 2 where the signal is analyzed under software control.

The present bus system can be configured in either an open or closed loop fashion, with each of the data points coupled to the bus 6, which may be a twisted pair cable, via the single point or the multiplexed transmitters 8, which will be described in more detail later. It is to be noted that the present embodiment is directed to an open loop system, which can accommodate up to eight buses at the bus multiplexer 4 with each bus 6 coupled to fifteen discrete data points and each data point having a four bit strapped address, A, hardwired to its associated transmitter 8. It is thus possible to accommodate 120 data points if all single point transmitters are used. If the multiplexed transmitters are used, the system can accommodate 192 data points, assuming three multiplexed and three single point transmitters per input of the bus multiplexer 4.
If the system is configured as a totally closed loop, it can accommodate either 60 or 92 data points, since the bus multiplexer 4 interrogates the same data points from each end of bus 6. The redundant closed loop system, however, enables the detection of failure conditions, such as the severing of the bus 6. The closed loop system also requires more processor time to sort the serial response signal received from the bus multiplexer 4 for each interrogation. The present invention, however, is not directed to the operations required within the processor 2, since they are primarily software oriented, and merely assumes that the processor 2 appropriately initiates the interrogation signals and that the consequent data handling operations occur under the control of processor 2, and are fixed at the time each system is configured.
The typical sequence of events that occur in the multiplexer during each interrogation cycle of the system will now be described with reference to each system element and the bus timing diagram of Figure 4. Referring also now to Figures 2, 3 and 4, as the line driver/receiver 10 receives the serial interrogation signal from the processor 2, which may be a ±5 volt Baudot code corresponding to the strapped address, A, of one data point coupled to each of the buses 6, it couples the signal to the asynchronous transceiver 12, driven by the 1.8 MHz clock 14, where the signal is converted into a parallel, five bit, binary interrogation signal. Once the conversion is complete, a data ready (DR) signal is transmitted to the low speed clock enable logic circuitry 17, which enables frequency divider 18 and causes transceiver 12 to clear and load the interrogation signal into counter decoder 16, thus presetting the down count of counter/decoder 16 at a value of m. The enabling of the frequency divider 18 causes frequency divider 18 to disable the logic circuitry 17 during the remainder of the interrogation cycle and load and initiate its counters such that it divides down the 1.8 MHz clock signal to produce a 7.03 KHz clock signal which is then used to clock counter/decoder 16 and pulse generator 20. It is also to be noted that the enabling of frequency divider 18 causes pulse generator 20 to produce one additional pulse. As counter/decoder 16 counts down from its preset m value, it causes pulse generator 20 to produce one pulse for each low speed clock cycle, approximately 140 µsec, for so long as the value in counter/decoder 16 is greater than or equal to zero. As a consequence, the bus multiplexer 4 produces a serial pulse train of m+1 pulses which is transmitted from each of the eight output ports of bus driver/receiver 22 to all the single point and multiplexed transmitters 8 coupled to the buses 6.
With the transmission of the last pulse during the zero count period, counter decoder 16 continues to count down to a value of A minus 6, which establishes a 770 µsec time period. During this time, the response pulse from each of the transmitters having the strapped address, A, corresponding to the number of pulses in the pulse train is received and transmitted to the processor 2. In particular, during the last half of the minus two count period, typically 28µ µsec later, counter/decoder 16 couples a transmit load, TL signal to the TL terminal of transceiver 12 which causes the response signals from the transmitter 8 waiting on the input ports A through J of bus driver/receiver 22 to be loaded into transceiver 12. The response signals are loaded in transceiver 12 in parallel but during the next 490 _flsec, while counter/decoder 16 counts down to minus 6, the response signals are transmitted via the line driver/receiver 10 in a serial fashion to the processor 2 for sorting and analysis. The 490 _flsec period also enables each of the transmitters 8 to clear prior to receipt of the next interrogation pulse train, thus preventing any spurious response pulses from being transmitted.
Prior to continuing the description of the detailed operation of the single point and multiplexed transmitters, a few design points should be noted. In particular, the least significant bit position, A_o, of the transmitter inputs are not used for address interrogation information, which dictates that m equal two times the value of the strapped address (m=2A) being interrogated. It should also be noted that, in the present system, the first pulse is not recognized by the transmitters 8 as part of an interrogation signal, but rather is used to initiate and load the transmitters 8 with their strapped address; the transmitters 8 therefore respond only if they receive two times the value of their strapped address plus one pulse. Further, to interrogate fully the status of any data point associated with a single point transmitter, it is necessary to transmit two pulse trains of (m+1) and (m+2) pulses in succession, and then compare the serial response signals in the processor 2 according to the interpretations of Table I
where the presence of a transmitter response pulse (i.e., a logic "low" on the bus 6) is interpreted to be a binary 1 and the absence of a response pulse (i.e., the bus remains at a logic "high") is interpreted to the binary zero. Note that an apparent error may occur because the status of the data point may have changed during interrogation in which event the processor can repeat the interrogation to determine if a change occurred or a fault exists. It should be further noted that the data signals are typically received simultaneously on the input ports of driver/receiver 22 with the response signals on each input port sequentially assigned, with A assigned the least significant bit position of the serial response signal and F assigned the most significant bit position.
Referring now to Figures 4, 5 and 6, the operation of a single point transmitter will be described. The same sequence of events occurs within each single point transmitter coupled to each of the buses 6. Upon receipt of the first pulse from the bus multiplexer 4, the receiver 24, which may be a Schmitt trigger, produces a noise free, square pulse which causes timer 28, which may be a retriggerable single shot, to being timing, and counter 26 to load its 4 bit strapped address, A, in complementary form, and the status input of its associated data point, which is coupled to the A_o bit position of counter 26. Once the Q terminal of timer 28 goes to a logic "high", counter 26 will count up on receipt of subsequent pulses. Each subsequent pulse will cause the counter 26 to advance and timer 28 to reset its time to zero. The Q terminal of timer 28 will thus remain "high" until approximately one pulse period beyond the end of the pulse train. Following the end of the pulse train, the binary signal on the terminal count, TC, terminal of counter 26 will correspond with the conditions established in Table II.
where X implies that the status does not matter.
When timer 28 times out, its Q terminal goes "high" and causes the signal at the TC terminal of counter 26 to be stored in the D flip-flop 33, and the Q terminal goes "low" and triggers timer 30. Timer 30, which consists of two series coupled single shots, will delay approximately one half clock pulse period, nominally 70 _jUsec, and then produce an output pulse of approximately one pulse period, nominally 140,usec. If the condition of the TC terminal of counter 26 is "high" (i.e., 2A+1 pulses and status of 0 or 2A+2 pulses and status of 1) terminal Q of the flip-flop 33 will be "high" and line driver 32, a logical NAND circuit, will transmit a "low" response signal, over the data bus 6 to the bus multiplexer 4. If the TC terminal is "low", a "high" response signal (i.e., the bus remains at a logic "high") will be transmitted.
If it is desired to use a single point transmitter as a data receiver rather than a data transmitter, the Q or Q terminal of the J-K flip-flop 35 is connected to the status input and the other to the data point's input and/or a monitor station and the operation of the transmitter remains the same as during normal data transmission operations. Assuming Q is coupled to the status input, if it is desired to set flip-flop 35, a pulse train of 2A+ 1 pulses is applied. If flip-flop 35 was previously set, the status on the Q terminal will be "low", the TC terminal of counter 26 coupled to the J and K inputs will be "low" and flip-flop 35 will remain set. If flip-flop 35 was previously cleared, the status on the Q terminal will be "high", the TC terminal of counter 26 will be "high" and flip-flop 35 will change state to the set condition. If it is desired to clear flip-flop 35, a pulse train of 2A+2 pulses is applied and the response will be similar to that described for setting the previously set or cleared flip-flop 35. Typically, however, the previous state of flip-flop 35 is known and the appropriate pulse train is applied to force a change of state and thereby affect the status of the data point.
Whenever a setting or clearing operation causes the flip-flop 35 to change state, a response signal is produced identical to that produced in normal data transmitter operation. This response signal is then observed by the processor 2 as a confirmation of the change of state. Thus it is possible to vary the output to selected data points and monitor the operation to ensure the change. It is to be recognised that during the operation of the single point transmitters as a data receiver, all but one of the NAND gates of bus driver/receiver 22 have their inputs disabled so that only one of the data points corresponding to the pulse train is affected.
It should also be recognised that the system's single point transmitters, as well as the multiplexed transmitters, are fabricated from low power, complementary metal-oxide semiconductor (CMOS) parts which enables each transmitter 8 to operate without a separate power supply. The transmitter, instead, derives its power from the interrogation pulse trains from the bus multiplexer 4 via the Vcc generator 34 which converts part of the energy in the pulse trains to a constant Vcc voltage which is coupled to the power pins of each part. Specifically, the Vcc generator consists of a series coupled diode-capacitor combination and the Vcc voltage is the voltage that develops across the capacitor.
While many systems have widely dispersed data points, the data points may in some cases be geographically concentrated. In such circumstances, a hardware saving can be achieved with the multiplexed transmitter shown in Figures. 7 and 8 and at the same time an increase in the number of addressable data points per bus multiplexer 4 input port and a reduction in interrogation time may be realised. The multiplexed transmitter achieves these ends by requiring fewer terminals per loop and fewer pulse trains to interrogate the data points coupled to the multiplexed transmitter. The multiplexed data points can be completely interrogated with eight pulse trains, whereas an equal number of single point transmitters requires fourteen pulse trains.
Referring now to Figures 7 and 8, a seven bit multiplexed transmitter is shown which comprises similar CMOS parts and operates in a similar fashion to the single data point transmitter previously described. The multiplexed transmitter requires four addresses to accommodate seven data points, whereas the single point transmitter required one address per data point. The seven data points are thus grouped and represented by four bit positions, but the least significant bit position of the strapped address now corresponds to a wired "high".
A typical sequence of events will now be described with reference to the selection of the status information on status input "0" and the transmission of the corresponding response signal. When the multiplexed transmitter receives the first pulse of the (2A+ 1) pulse train, timer 38, which may be a retriggerable single-shot, is initiated and counter 36 is loaded with strapped address A in complementary form, thus permitting counter 36 to count on the successive pulses. Since the address being interrogated with the (2A+1 ) pulse train corresponds to the status input "0", the strapped address will match the count and the TC terminal will indicate a logic "high" at the end of the pulse train. When timer 38 times out, approximately one pulse period after the interrogation pulse train, timer 40 is initiated and produces a logic "high" which remains approximately one-half pulse period. The logic "high" from counter 36 and timer 40 then cause register 44 to impress the status inputs "0" through "6" of the seven discrete data points on the inputs Do to D₅ and D, of multiplexer 46. At the same time, three bits of the count information in counter 36 (i.e., a binary 111) corresponding to status input "0" bit position in register 44 are impressed on the select inputs A_o through A₂ of multiplexer 46 and four bits indicating a match of the strapped address are impressed on decoder 42, causing decoder 42 to produce a logic "high".
Upon timer 40 timing out, a logic "low" is produced which causes timer 48 to begin timing and produce a logic "high". NAND gate 50 responding to the logic "high's" from timer 48 and decoder 42 produces a logic "low" which enables multiplexer 46 to select the information resident at its D, bit position which corresponds to the status input "0".
Table III shows the effects of the pulse trains of (2A+2) through (2A+8), which are used to interrogate the remaining status bits 1 through 6, and parity bit 7. It is to be noted that register 44 is loaded only on the (2A+1 ) pulse train, since typically the processor 2 interrogates each strapped address sequentially.
Once the information in the status input "0" bit position is selected, it is next stored in flip-flop 51. This occurs since decoder 42 produces a logic "high" on its output terminal W for each of the eight sequential pulse trains of Table III, thus as timer 48 goes "high", NAND gate 50 will cause multiplexer 46 to load flip-flop 51. If a logic "high" is present on the selected status input or parity bit position of multiplexer 46, flip-flop 51 will set for the duration of the timer 48 "high" output. The resulting "high" output on the Q terminal of set flip-flop 51 will then cause line driver 52 to produce a logic "low" which will be transmitted to multiplexer 4. In a similar manner, if flip-flop 51 is cleared, a logic "high" is transmitted.
As the status inputs are sequentially addressed, an "odd" parity bit, associated with the D₆ bit position of multiplexer 46, is also generated in the following manner: at the time register 44 is first loaded, the parity flip-flop 54 is cleared which indicates that an even number of "1 's" (zero at this point in time) have been transmitted. However, when a "1" is transmitted, its trailing edge, signified by the Q terminal of flip-flop 51 going "low", causes the parity flip-flop 54 to toggle (i.e., reverse status). Thus the transmission of an odd number of "ones" will leave the parity flip-flop 54 set; an even number will leave it cleared. When the parity bit is selected on the (2A+8) pulse train, the status of the Q terminal of flip-flop 54 is selected by the multiplexer 46. If an even number of "1's" has been transmitted, Q will be "high" thus transmitting an additional "1 ". If an odd number of ones has been transmitted, will be "low" and "0" will be sent. It should be noted that the processor can cause failure of the parity generation by failing to perform the interrogations in the order indicated, but the processor is considered to be "smart" enough not to do this.
The bus multiplexer 4, on receipt of the interrogated transmitter's response signals at input ports A through F, transmits the information in the manner previously described back to processor 2 via the asynchronous transceiver 12 and line driver/receiver 10. The processor 2, under software or firmware control, then processes the information, which activity is dependent on the configuration of the system selected from the possible permutations of transmitters on each of the open or closed loop data buses 6.

Claims

1. A status reporting system comprising a processor (2) and a plurality of data transmitters (8) each associated with a data point, and each coupled to a bus (6), characterised in that the processor (2) and a plurality of buses (6) are coupled to a signal processing and bus multiplexing device (4) which includes means (16, 17, 18, 20, 22) responding to a signal from the processor (2), for sending out interrogation signals on each bus (6) simultaneously, and means (22, 16, 12) for transmitting the responses of the interrogated transmitters (8) received over the buses (6) serially to the processor (2).

2. A status reporting system according to claim 1 in which at least one of the transmitters (8) includes means (35) for changing the status of its associated data point in response to an interrogation signal, and means (33) for verifying the change of status to the processor.

3. A status reporting system according to claim' 1 or claim 2 further characterised in that it includes at least one multiplexed transmitter (Figure 8a, 8b) coupled to a group of data points, the multiplexed transmitter (having a group address, and being arranged to transmit the status of selected data points of the group after being interrogated with the group address.

4. A status reporting system according to any preceding claim characterised in that the transmitters (8) are of low power consumption and are each provided with a circuit (34) for deriving the power for operating the transmitter from the interrogation signals.

5. A data transmitter (8) suitable for use in a system according to any preceding claim connected to a bus (6), and arranged to respond when addressed by a train of uniformly-spaced pulses characterised in that it comprises a timer (28, Figure 4), (38, Figure 7), set to time out at the end of the pulse train, a counter (26, Figure 4), (38, Figure 7), counting the received pulses, means (24) for loading the counter with an address on receipt of the initial pulse on the pulse train, and means (30, 32, 33, Figure 4), (48, 50, Figure 7), for initiating the transmission of a response if the contents of the counter (26) stand at its terminal count when the timer (28, 38) times out.

6. A multiplexed data transmitter according to claim 5 further characterised in that it includes a register (44) loaded with status inputs from its associated data points when the timer (38) times out and the counter (36) stands at its terminal count, and that a multiplexer (46) transmits the status inputs over the bus (6) in response to successive address signals on the bus.